Exhaust muffler for vehicle

ABSTRACT

An exhaust muffler for a vehicle includes a muffler body coupled to an exhaust pipe and a tailpipe coupled to the muffler body. The muffler body has a plurality of expansion chambers, an exit communication pipe that discharges exhaust to the tailpipe from one of the plurality of expansion chambers positioned in a most downstream part of an exhaust flow path, and a spark arrester arranged in the exit communication pipe. An exhaust flow path narrowing portion is provided at an entrance portion of the exit communication pipe.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an exhaust muffler for a vehicle. Inparticular, the present invention relates to a spark arrester providedin an exhaust muffler for a vehicle.

2. Description of the Related Art

Conventionally, an exhaust muffler for a vehicle including a sparkarrester is known. In general, the spark arrester is formed by amesh-like member made of metal.

Meanwhile, since the spark arrester is arranged in an exhaust flow pathin the exhaust muffler and exposed to exhaust gas, it is required to beso durable that it does not deform under conditions of high temperaturesand high back pressure with an exhaust pulse. Accordingly, the sparkarrester is provided with a frame member for reinforcing a mesh-likemember made of a metal mesh. Thus, the spark arrester is prevented fromdeforming under the foregoing conditions. There is Prior TechniqueDocument JP 8-61046 A.

That is, the spark arrester is structured by a mesh-like member as afilter portion, and a frame member as a reinforcing portion forreinforcing the filter portion. Therefore, since the structure iscomplicated, manufacturing of the spark arrester is not easy andinvolves high costs.

SUMMARY OF THE INVENTION

The present invention is made in consideration of the foregoingproblems, and an object thereof is to provide an exhaust muffler for avehicle including a spark arrester, designing of which can bestreamlined.

In order to achieve the object stated above, the present inventionprovides an exhaust muffler for a vehicle including a muffler bodycoupled to an exhaust pipe, and a tailpipe coupled to the muffler body.The muffler body includes a plurality of expansion chambers, an exitcommunication pipe that discharges exhaust to the tailpipe from one ofthe plurality of expansion chambers positioned in a most downstream partof an exhaust flow path, and a spark arrester arranged in the exitcommunication pipe. An exhaust flow path narrowing portion is providedat an entrance portion of the exit communication pipe.

With the structure described above, the spark arrester is not arrangedin the expansion chamber but in the exit communication pipe. Further,the exhaust flow path narrowing portion is provided at the entranceportion of the exit communication pipe. Thus, the back pressure actingon the spark arrester can be reduced, whereby deformation due to backpressure of the spark arrester can be suppressed. As a result, thereinforce member can be dispensed with, and designing of the sparkarrester can be streamlined.

With the exhaust muffler, preferably, the following structure can beemployed.

(1) .The spark arrester is structured by a mesh-like member.

With the structure (1), since the spark arrester is structured by amesh-like member, the productivity of the spark arrester can be improvedand costs can be reduced.

Furthermore, since no reinforce member covers the surface of the sparkarrester, the filter portion of the spark arrester can be secured forthe entire surface. As a result, the spark arrester can be structured ina compact manner.

(2) The exhaust flow path narrowing portion is structured by a lidmember that has a through hole and that is provided at an upstreamportion of the exit communication pipe.

With the structure (2), the exhaust flow path narrowing portion can beeasily formed. Further, as compared with the case where a taperednarrowing portion is formed, the exhaust flow path can be sharplynarrowed, and the back pressure in the exit communication pipe can bemore effectively reduced. Thus, deformation caused by the back pressureof the spark arrester can be further suppressed.

(3) In the structure (2), the opening area of the through hole issubstantially identical to the cross-sectional area of the exhaust flowpath at the upstream end of the exhaust pipe.

With the structure (3), while realizing a reduction in the backpressure, it becomes possible to secure the exhaust flow path of propersize, and to avoid a reduction in the engine performance attributed toan excessive increase in the back pressure.

(4) In the structure (2), the difference between the cross-sectionalarea being perpendicular to the exhaust flow path of the exitcommunication pipe and the cross-sectional area being perpendicular tothe exhaust flow path of the spark arrester is substantially identicalto an opening area of the through hole.

With the structure (4), it becomes possible to avoid an excessiveincrease in the diameter of the exit communication pipe, whereby themuffler body can be structured in a compact manner.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a left side view of a utility vehicle according to oneembodiment;

FIG. 2 is a perspective view of an exhaust system;

FIG. 3 is a left side view of an exhaust muffler;

FIG. 4 is an exploded perspective view of the exhaust muffler;

FIG. 5 is a V-V cross-sectional view of the exhaust muffler shown inFIG. 3;

FIG. 6 is a VI-part enlarged view of the exhaust muffler shown in FIG.5;

FIG. 7 is a VII-part enlarged view of the exhaust muffler shown in FIG.5;

FIG. 8 is a vertical cross-sectional view of a spark arrester;

FIG. 9 is a IX-IX cross-sectional view of the exhaust muffler shown inFIGS. 5; and

FIG. 10 is a X-X cross-sectional view of the exhaust muffler shown inFIG. 5.

DETAILED DESCRIPTION OF THE INVENTION Embodiment [Overall Structure]

In the following, with reference to the accompanying drawings, adescription will be given of one embodiment of the present invention.Note that, for the sake of convenience in describing, the followingdescription is based on the premise that the front-rear direction of avehicle is applied to the front-rear direction of the exhaust mufflerand other components, and that the right-left direction in connectionwith the vehicle-width direction (the right and left sides as seen fromthe rear of the vehicle) as seen from the passengers on the vehicle isapplied to the right-left direction of the exhaust muffler and othercomponents.

FIG. 1 is a left side view of a utility vehicle according to the presentembodiment, with shell constituent members such as doors being removed.As shown in FIG. 1, the utility vehicle includes: a right and left pairof front wheels 11 on the front side and a right and left pair of rearwheels 12 on the rear side; a passenger space 14 surrounded by a ROPS13, between the front wheels 11 and the rear wheels 12; and a rear deck15 on the rear side of the passenger space 14. The ROPS 13 is anabbreviation for a rollover protective structure.

In the passenger space 14, a floor panel 16 forming the floor surface, afront seat 17, and a rear seat 18 are provided. Below the rear seat 18,an engine 20 is stored. In front of the engine 20, an exhaust portion 21for discharging exhaust gas is provided. To the exhaust portion 21, anexhaust system 1 is connected, and the exhaust gas discharged from theengine 20 is purified by the exhaust system 1 with exhaust noises beingcancelled, and discharged into the air.

[Exhaust System 1]

With reference to FIG. 2, a description will be given of the exhaustsystem 1. FIG. 2 is a perspective view of the exhaust system 1, togetherwith the engine 20 and a transmission 22. As shown in FIG. 2, theexhaust system 1 includes an exhaust pipe 7 fixed to an exit portion ofthe exhaust portion 21 via a flange 71, and an exhaust muffler 2 beingfixed by welding to the downstream end portion of the exhaust pipe 7.The exhaust muffler 2 is arranged at the substantially center portion inthe vehicle-width direction and below the rear deck 15 (see FIG. 1). Theexhaust muffler 2 is mounted on an exhaust muffler mounting portion 24mounted at an upper portion of the transmission 22, via an exhaustmuffler mounting apparatus 8.

The exhaust muffler mounting portion 24 has a support bracket 241 fixedto the upper portion of the transmission 22, and rod engaging portions242 fixed by welding to the top face of the support bracket 241. The rodengaging portions 242 are provided to form a right and left pair, andeach provided with a rubber damper 242 a having a bore penetrating inthe front-rear direction. Into the bore of the rubber damper 242 a, arod 82 of the exhaust muffler mounting apparatus 8 is inserted in thefront⁻rear direction, whereby the exhaust muffler 2 is held.

[Exhaust Pipe 7]

The exhaust pipe 7 extends from the flange 71, via a pipe 70 beingcurved to detour the engine 20 from the left side toward the rear side,and reaches the exhaust muffler 2 via an entrance cone portion 73. Onthe outer surface of the pipe 70, a heat shield plate 72 is attached,whereby heat is prevented from dissipating from the surface of the pipe70 to the surrounding components. To the entrance cone portion 73, asensor mounting boss 74 (see FIG. 3) for mounting an exhaust gas sensoris provided.

[Exhaust Muffler 2]

With reference to FIGS. 3 to 7, a description will be given of theexhaust muffler 2. FIG. 3 is a left side view of the exhaust muffler 2.FIG. 4 is an exploded perspective view of the exhaust muffler 2. FIG. 5is a V-V cross-sectional view of FIG. 3. FIG. 6 is a VI-part enlargedview of FIG. 5. FIG. 7 is a VII-part enlarged view of FIG. 5. In FIG. 4,a sleeve portion 30 and the downstream side cover 34 are partiallytransparent to show the internal structure, and the exhaust mufflermounting apparatus 8 is not shown.

As shown in FIG. 3, the exhaust muffler 2 includes a muffler body 3, aspark arrester 5 mounted on the rear portion of the muffler body 3, andthe exhaust muffler mounting apparatus 8 mounted on the bottom portionof the muffler body 3. As shown in FIG. 4, a gasket 9 is assembledbetween the spark arrester 5 and the muffler body 3.

(Muffler Body 3)

The muffler body 3 has a shell formed by the sleeve portion 30, anupstream side cover 33 closing the upstream side opening of the sleeveportion 30, and a downstream side cover 34 closing the downstream sideopening of the sleeve portion 30. At the upstream side cover 33, anexhaust entrance portion 332 connected to the entrance cone portion 73of the exhaust pipe 7 (see FIG. 2) is formed. At the downstream sidecover 34, an exhaust exit portion 342 to which a spark arrester 5 isconnected is formed.

In the muffler body 3, an upstream side separator 35 and a downstreamside separator 36 are provided. A second expansion chamber 38 is formedbetween the upstream side cover 33 and the upstream side separator 35,and a first expansion chamber 37 is formed between the upstream sideseparator 35 and the downstream side separator 36. By the provision ofthe downstream side separator 36, the downstream side of the exhaustmuffler body 3 becomes the double structure, and a heat insulationchamber (or a sound shield chamber) 39 is formed between the downstreamside separator 36 and the downstream side cover 34. That is, in themuffler body 3, the second expansion chamber 38, the first expansionchamber 37, and the heat insulation chamber 39 are formed in turn fromthe front side.

Further, the muffler body 3 is provided with an entrance communicationpipe 40 communicatively connecting between the exhaust entrance portion332 and the first expansion chamber 37, and an exit communication pipe41 communicatively connecting between the second expansion chamber 38and the exhaust exit portion 342.

Next, a specific description will be given of the constituent elementsof the muffler body 3.

Upstream Side Cover 33

The upstream side cover 33 has a front wall 331, an exhaust entranceportion 332 formed at the substantially left half surface of the frontwall 331, and an upstream side cover flange portion 333 projectingrearward from the circumference of the front wall 331. At thesubstantially right half surface of the front wall 331, a substantiallyX-shaped reinforcing bead 331 a projecting frontward is formed.Formation of the reinforcing bead 331 a improves the surface stiffnessof the front wall 331, whereby vibration noises (chattering noises) ofthe front wall 331 are suppressed. Furthermore, as the reinforcing bead331 a is formed so as to project frontward, the volume of the mufflerbody 3 increases.

As shown in FIG. 5, the exhaust entrance portion 332 has a burring-likeopening shape projecting frontward, and has its front portion externallyfitted to the outer circumference face of the entrance communicationpipe 40. The front end portion of the exhaust entrance portion 332 ispositioned rearward than the front end portion of the entrancecommunication pipe 40.

Referring back to FIG. 4, the upstream side cover flange portion 333 hasan upstream side inner sleeve holding portion 333 a projecting rearwardfrom the periphery of the front wall 331, and an upstream side outersleeve holding portion 333 c projecting rearward from the upstream sideinner sleeve holding portion 333 a via an upstream side step portion 333b. The upstream side outer sleeve holding portion 333 c is positionedradially outward than the upstream side inner sleeve holding portion 333a.

Downstream Side Cover 34

The downstream side cover 34 has a rear wall 341, an exhaust exitportion 342 formed at the substantially right half surface of the rearwall 341 and a downstream side cover flange portion 343 projectingfrontward from the periphery of the rear wall 341. At the substantiallyleft half surface of the rear wall 341, a substantially X-shapedreinforcing bead 341 a projecting rearward is formed. Formation of thereinforcing bead 341 a improves the surface stiffness of the rear wall341, whereby vibration noises (chattering noises) of the rear wall 341are suppressed. Furthermore, as the reinforcing bead 341 a is formed soas to project rearward, the volume of the muffler body 3 increases.

The exhaust exit portion 342 has a gasket mounting face 342 a formed ina concave manner frontward from the rear wall 341, an exhaust exitopening 342 b bored at the gasket mounting face 342 a, and a sparkarrester mounting portion 342 c provided on the rear wall 341 radiallyoutward than the gasket mounting face 342 a.

The downstream side cover flange portion 343 has a downstream side innersleeve holding portion 343 a projecting frontward from the periphery ofthe rear wall 341, and a downstream side outer sleeve holding portion343 c further projecting frontward from the downstream side inner sleeveholding portion 343 a via a downstream side step portion 343 b. Thedownstream side outer sleeve holding portion 343 c is positionedradially outward than the downstream side inner sleeve holding portion343 a.

Sleeve portion 30

As shown in FIG. 5, the sleeve portion 30 includes an outer sleeve 31,an inner sleeve 32 positioned as being distanced from the outer sleeve31 radially inwardly, and a sound absorption chamber 42 formed betweenthe outer sleeve 31 and the inner sleeve 32. A sound absorbing material43 is enclosed in the sound absorption chamber 42. The sound absorbingmaterial 43 has, for example, a two-layer structure, and is structuredby stainless steel wool arranged on the inner sleeve 32 side and glasswool arranged on the outer sleeve 31 side. Note that, the soundabsorbing material 43 may be formed in a single-layer structure.

The outer sleeve 31 is a cylindrical element formed of a steel platebeing wound in an elliptical manner, the abutting ends of which arejoined to each other by welding. The outer sleeve 31 extends from theupstream side outer sleeve holding portion 333 c to the downstream sideouter sleeve holding portion 343 c. The front portion of the outersleeve 31 is fixed by welding to the rear end peripheral portion of theupstream side outer sleeve holding portion 333 c, and the rear portionof the outer sleeve 31 is fixed by welding to the front end peripheralportion of the downstream side outer sleeve holding portion 343 c.

The inner sleeve 32 is a cylindrical element formed of a steel platebeing wound in an elliptical manner, the abutting ends of which arejoined to each other by welding. The inner sleeve 32 extends from theupstream side inner sleeve holding portion 333 a to the downstream sideinner sleeve holding portion 343 a. The front portion of the innersleeve 32 has its outer circumferential cylindrical face internallyfitted to the upstream side inner sleeve holding portion 333 a so as tobe slidable in the front-rear direction (that is, in the longitudinaldirection of the muffler body 3). On the other hand, the rear portion ofthe inner sleeve 32 is fixed by welding at several portions in thecircumferential direction, as being interposed between the downstreamside separator flange portion 362 and the downstream side inner sleeveholding portion 343 a.

Since the inner sleeve 32 is held in this manner, the relativeelongation between the outer sleeve 31 and the inner sleeve 32 can betolerated. That is, when exhaust gas flows inside the exhaust mufflerbody 3, the outer sleeve 31 and the inner sleeve 32 thermally expand inaccordance with their respective temperatures. Meanwhile, the sleeveportion 30 has a double structure made up of the outer sleeve 31 and theinner sleeve 32, and furthermore, the sound absorbing material 43 isarranged between the outer sleeve 31 and the inner sleeve 32.Accordingly, the outer sleeve 31 and the inner sleeve 32 are differentfrom each other in temperature. More specifically, the temperature ofthe inner sleeve 32 facing the first and second expansion chambers 37and 38 and the heat insulation chamber 39 is higher than that of theouter sleeve 31 being exposed to the air. Therefore, the thermalexpansion amount of the inner sleeve 32 is greater than that of theouter sleeve 31.

At this time, the upstream side cover 33 and the downstream side cover34 become away from each other in accordance with the thermal expansionamount of the outer sleeve 31, and the inner sleeve 32 having its rearportion fixed to the downstream side cover 34 shifts with the downstreamside cover 34. On the other hand, the front portion of the inner sleeve32 slides over the upstream side inner sleeve holding portion 333 a ofthe upstream side cover 33 and thermally expands freely, irrespective ofthe displacement of the upstream side cover 33 corresponding to thethermal expansion amount of the outer sleeve 31. That is, the relativeelongation of the outer sleeve 31 and the inner sleeve 32 is tolerated.

Further, the inner sleeve 32 is provided with many pores 322 thatestablish communication between the sound absorption chamber 42 and thesecond expansion chamber 38. Further, as shown in FIG. 6 in an enlargedmanner, at the front end portion of the inner sleeve 32, a bent portion321 that is inwardly bent is formed. Formation of the bent portion 321allows the inner sleeve 32 to be easily assembled to the upstream sideinner sleeve holding portion 333 a. Specifically, allowing the bentportion 321 to abut on the entrance portion of the upstream side innersleeve holding portion 333 a, the inner sleeve 32 can be guided andassembled to the upStream side inner sleeve holding portion 333 a.

Thus, for example in the case where the upstream side cover 33 is fixedby welding to the outer sleeve 31 and thereafter the inner sleeve 32 isassembled from the downstream side of the outer sleeve 31, the tipportion of the inner sleeve 32 can be easily fitted to the upstream sideinner sleeve holding portion 333 a at the bottom while being guided bythe bent portion 321. That is, the inner sleeve 32 can be easily fittedto the upstream side inner sleeve holding portion 333 a at the bottomthat cannot easily be visually recognized.

Upstream Side Separator 35

Referring back to FIG. 5, the upstream side separator 35 has an upstreamside partition wall 351 that partitions the inner circumferential sideof the inner sleeve 32 into the first expansion chamber 37 and thesecond expansion chamber 38, and an upstream side separator flangeportion 352 projecting rearward from the periphery of the upstream sidepartition wall 351. At the upstream side partition wall 351, aburring-like entrance communication pipe mounting portion 351 a and anexit communication pipe mounting portion 351 b projecting rearward, anda burring-like communication hole 351 c projecting frontward (see FIG.4) are formed. The upstream side separator 35 is fixed by welding atseveral portions in the circumferential direction to the innercircumferential face of the inner sleeve 32 via the upstream sideseparator flange portion 352.

Downstream Side Separator 36

The downstream side separator 36 has a downstream side partition wall361 that partitions the inner circumferential side of the inner sleeve32 into the first expansion chamber 37 and the expansion chamber 39, anda downstream side separator flange portion 362 projecting rearward fromthe periphery of the downstream side partition wall 361. At thedownstream side partition wall 361, a burring-like exit communicationpipe mounting portion 361 a projecting rearward is formed. Thedownstream side separator 36 is fixed to the downstream side innersleeve holding portion 343 a by welding, together with the rear portionof the inner sleeve 32 as described above, at several portions in thecircumferential direction via the downstream side separator flangeportion 362.

Entrance Communication Pipe 40

The entrance communication pipe 40 is made of a straight tubular pipemember having a constant diameter, and extends rearward from the exhaustentrance portion 332, to the rear side of the entrance communicationpipe mounting portion 351 a. In the entrance communication pipe 40, acatalyst 6 is arranged. As shown in FIG. 7 in an enlarged manner, thefront end portion of the exhaust entrance portion 332 and the front endportion of the entrance communication pipe 40 are arranged stepwise onthe outer circumference of the entrance cone portion 73, and these threecomponents are integrally joined by a common welding bead W1. Referringback to FIG. 5, the rear portion of the entrance communication pipe 40is joined by welding at several portions in the circumferentialdirection to the entrance communication pipe mounting portion 351 a.

Catalyst 6

The catalyst 6 is structured by a first catalyst 61 and a secondcatalyst 62, in each of which a honeycomb carrier made of metal issupported noble metal. The second catalyst 62 has its downstream sideend face substantially matched with the downstream end portion of theentrance communication pipe 40. The first catalyst 61 is arranged to beaway on the upstream side by a prescribed distance relative to thesecond catalyst 62.

Distance L1 between the upstream side end face of the first catalyst 61and the downstream side end face of the second catalyst 62 issufficiently shorter than length L2 of the entrance communication pipe40. For example, distance L1 is set to be substantially half as great asL2. That is, in front of the first catalyst 61 in the entrancecommunication pipe 40, a space having a substantially identical innerdiameter as the outer diameter of the first catalyst 61 is formed over aprescribed length.

The first catalyst 61 and the second catalyst 62 are fixed by brazing tothe inner circumferential face of the entrance communication pipe 40.

Exit Communication Pipe 41

The exit communication pipe 41 has a straight tubular pipe member 411having a constant diameter, and a lid member 412 joined by welding tothe front end portion of the pipe member 411. The pipe member 411extends from the front of the exit communication pipe mounting portion351 b to immediately before the exhaust exit portion 342 via the exitcommunication pipe mounting portion 361 a. Note that, the central axisof the pipe member 411 is substantially identical to the central axis ofthe exhaust exit opening 342 b. The rear end position of the pipe member411 is set so as not to be in contact with the exhaust exit portion 342,in consideration of the shape tolerance, the assembly tolerance, thethermal expansion amount and the like of each component.

At the lid member 412, a burring-like opening 412 a projecting frontwardis formed. The exit communication pipe 41 is fixed by welding at severalportions in the circumferential direction to the exit communication pipemounting portion 351 b of the upstream side separator 35 at a slightlyfrontward position than the central portion in the front-rear directionof the pipe member 411. Further, the exit communication pipe 41 is fixedby welding at several portions in the circumferential direction, on therear portion of the pipe member 411, to the exit communication pipemounting portion 361 a of the downstream side separator 36.

(Spark Arrester 5)

Next, a description will be given of the spark arrester 5 with referenceto FIGS. 8 to 10. FIG. 8 is a vertical cross-sectional view of the sparkarrester 5. FIG. 9 is a IX-IX cross-sectional view of FIG. 5. FIG. 10 isa X-X cross-sectional view of FIG. 5. As shown in FIG. 8, the sparkarrester 5 includes a spark arrester body portion 51 for capturing sootor carbon in exhaust gas, a tailpipe 52 for discharging the exhaust gashaving passed through the spark arrester body portion 51 into the air, aspark arrester flange 53 for mounting the spark arrester 5 to theexhaust exit portion 342 (see FIG. 4), an inner circumferential ring 54for coupling the spark arrester body portion 51 and the tailpipe 52 toeach other, and an outer circumferential ring 55 for fixing the sparkarrester body portion 51 to the inner circumferential ring 54.

The spark arrester body portion 51 is in a shape of a sleeve whose frontend portion is closed while being open rearward. The circumference ofthe spark arrester body portion 51 is formed by having a mesh-likemember made of metal cylindrically wrapped around such that its oppositeperipheries overlap each other, and by fixing the overlapped peripheriesat several portions by spot welding. Then, as shown in FIG. 9, the frontportion of the spark arrester body portion 51 is formed by folding foursides of the circumferential portion inwardly, and fixing thesubstantially center portion of the overlapped mesh-like member by spotwelding.

Referring back to FIG. 8, the tailpipe 52 is a pipe-like member, whichextends rearward, and then curves diagonally downward. Thus, exhaust gasis caused to be discharged from the rear end portion of the tailpipe 52in the rearward diagonally downward direction, that is, toward theground.

The spark arrester flange 53 includes a substantially triangular baseplate 531 (see FIG. 4), a sidewall 532 provided to stand rearward fromthe periphery of the base plate 531, and a tailpipe mounting portion 533provided at the substantially center portion of the base plate 531 so asto project rearward. Near each vertex of the substantially triangle baseplate 531, a spark arrester mounting hole 531 a is bored. As shown inFIG. 4, by allowing a bolt 10 to penetrate through the spark arrestermounting hole 531 a so as to screw to the spark arrester mountingportion 342 c, the spark arrester 5 is removably fixed to the exhaustexit portion 342. Further, as shown in FIG. 5, the spark arrester bodyportion 51 is positioned in the exit communication pipe 41 in the statewhere the spark arrester 5 is fixed to the muffler body 3.

Referring back to FIG. 8, the outer circumferential ring 55 is acylindrical element opening in the front-rear direction, and is fittedto the outer circumferential portion of the spark arrester body portion51 with its rear end portion substantially matched with the rear endportion of the spark arrester body portion 51. The inner circumferentialring 54 is a cylindrical element that opens in the front-rear directionand that is structured to be longer in the longitudinal direction thanthe outer circumferential ring 55. The inner circumferential ring 54 isfitted to the inner circumferential portion of the spark arrester bodyportion 51 while being substantially matched with the front end portionof the outer circumferential ring 55. That is, the rear end portion ofthe inner circumferential ring 54 is positioned on the rear side of thespark arrester body portion 51.

By allowing the rear end portion of the spark arrester body portion 51to be inserted between the inner circumferential ring 54 and the outercircumferential ring 55, and fixing the inner circumferential ring 54and the outer circumferential ring 55 to each other by spot welding, thespark arrester body portion 51 made of a mesh-like member is surelyfixed to the inner circumferential ring 54 and the outer circumferentialring 55 each being a plate-like member.

At the rear portion of the inner circumferential ring 54, the tailpipe52 is fitted to the inner circumferential side, and the tailpipemounting portion 533 of the spark arrester flange 53 is fitted to theouter circumferential side. The rear end portion of the tailpipemounting portion 533 is positioned slightly frontward relative to therear end portion of the inner circumferential ring 54. Thus, the rearend portion of the tailpipe mounting portion 533 and the rear endportion of the inner circumferential ring 54 are arranged stepwise onthe outer circumference face of the tailpipe 52, and these threecomponents are integrally joined by a common welding bead W2.

Here, with reference to FIGS. 9 and 10, a description will be given of across-sectional area of the exhaust flow path defined by the sparkarrester 5 and the exit communication pipe 41. Firstly, with referenceto FIG. 9, the opening area S1 of the opening 412 a is designed to besubstantially identical to the cross-sectional area S2 (see FIG. 2) ofthe exhaust flow path at the upstream end of the exhaust pipe 7.Further, with reference to FIG. 10, the inner diameter of the pipemember 411 is set such that the difference between the cross-sectionalarea S3 being perpendicular to the exhaust flow path of the pipe member411 and the cross-sectional area S4 being perpendicular to the exhaustflow path of the spark arrester body portion 51 becomes substantiallyidentical to the opening area S1 (see FIG. 9) of the opening 412 a. Thatis, for the cross-sectional area of the exhaust flow path defined by thespark arrester 5 and the exit communication pipe 41, the cross-sectionalarea S2 of the exhaust flow path at the upstream end of the exhaust pipe7 is secured.

(Exhaust Muffler Mounting Apparatus 8)

Next, a description will be given of the exhaust muffler mountingapparatus 8. As shown in FIG. 9, the exhaust muffler mounting apparatus8 includes a metal-made rod support plate 81 fixed by welding to theouter circumference face of the outer sleeve 31, and a right and leftpair of metal-made rods 82 fixed by welding to the bottom end portion ofthe rod support plate 81. The rod support plate 81 has a first inclinedportion 811 extending from the right lower portion of the outer sleeve31 in the diagonally left downward direction, a second inclined portion812 extending from the left lower portion of the outer sleeve 31 in thediagonally right downward direction, and a horizontal portion 813 thatconnects between the bottom ends of the first and second inclinedportions 811 and 812 and that extends substantially horizontally. Therods 82 extend in the front-rear direction.

The first and second inclined portions 811 and 812 are respectivelyprovided with reinforcing beads 811 a and 812 a provided in thedirection being away from the outer sleeve 31 in a concave manner.Further, the horizontal portion 813 is provided with rod mountingportions 813 a for mounting the rods 82 and a reinforcing bead 813 bprovided in a concave manner toward the outer sleeve 31. The rodmounting portions 813 a are formed as a right and left pair. Thereinforcing bead 813 b is formed over the joining portion of thehorizontal portion 813 and the first and second inclined portions 811and 812. Provision of the reinforcing beads 811 a, 812 a, and 813 bimproves rigidity of the rod support plate 81.

Further, since the reinforcing beads 811 a and 812 a are provided in aconcave manner in the direction being away from the outer sleeve 31, thereinforcing beads 811 a and 812 a are prevented from abutting on theouter surface of the outer sleeve 31, whereby the first and secondinclined portions 811 and 812 can easily conform to the outer surface ofthe outer sleeve 31. Thus, the first and second inclined portions 811and 812 can be more surely fixed by welding to the outer sleeve 31.

Further, since the reinforcing bead 813 b is provided in a concavemanner toward the outer sleeve 31, the reinforcing bead 813 b isprevented from abutting on the outer surface of the rods 82, whereby therod mounting portions 813 a can easily conform to the outer surface ofthe rods 82. Thus, the rods 82 can be more surely fixed by welding tothe rod mounting portions 813 a.

As shown in FIG. 2, by allowing the right and left pair of rods 82 to beinserted into the bores of the rubber dampers 242 a of the exhaustmuffler mounting portion 24 mounted on the transmission 22 from the rearside toward the front side, the exhaust muffler 2 can be surely heldabove the transmission 22.

The exhaust system 1 has its front portion fixed to the exhaust portion21 of the engine 20 via the flange 71, and has its rear portion fixed tothe exhaust muffler mounting portion 24 provided to the transmission 22via the exhaust muffler mounting apparatus 8. Further, the transmission22 is fixed to the engine 20 so as not to be relatively displaced. Thatis, since the exhaust system 1 including the front portion and the rearportion is fixed to the identical vibration system, it is not necessaryto take into consideration of the relative displacement that occurs whenthe front portion and the rear portion are fixed to separate vibrationsystems. Thus, the exhaust system 1 is strongly fixed.

Further, since the exhaust muffler 2 is held by the rubber dampers 242 aas being inserted in the front-rear direction via the rods 82, thermalelongation of the exhaust system 1 in the front-rear direction,dimensional variations in the front-rear direction of each component ofthe exhaust system 1, or assembly variations of each component areabsorbed in an excellent manner.

(Gasket 9)

As shown in FIG. 4, the gasket 9 is a disc-like seal member exhibitingexcellent heat resistance. The gasket 9 seals against leakage of exhaustgas from between the gasket mounting face 342 a of the exhaust exitportion 342 and the base plate 531 of the spark arrester flange 53.

[Flow of Exhaust Gas]

Next, a description will be given of the flow of exhaust gas in theexhaust system 1. Firstly, as indicated by arrow A in FIG. 2, exhaustgas discharged from the exhaust portion 21 of the engine 20 passesthrough the exhaust pipe 7 and arrives at the exhaust muffler 2. At thistime, the exhaust gas enters from the entrance cone portion 73 of theexhaust pipe 7 and arrives at the exhaust entrance portion 332 (see FIG.3). Here, as indicated by arrow B in FIG. 5, since the entrance coneportion 73 has a cone shape whose diameter widens rearward, the exhaustgas passing through the entrance cone portion 73 arrives at the exhaustentrance portion 332 while substantially uniformly diffusing in theradial direction.

Next, as indicated by arrow C in FIG. 5, the exhaust gas flows into theentrance communication pipe 40. Since the catalyst 6 is arranged asbeing away by a prescribed length from the upstream side end portion ofthe entrance communication pipe 40, the exhaust gas is further diffusedin the radial direction while proceeding in the entrance communicationpipe 40 until it arrives at the catalyst 6. As a result, at the upstreamside end face of the catalyst 6, the exhaust gas that is substantiallyevenly distributed in the radial direction arrives.

Next, as indicated by arrow D in FIG. 5, the exhaust gas purified by thecatalyst 6 arrives at the first expansion chamber 37. At this time, thetemperature of the exhaust gas increases by the oxidation-reductionreaction of the catalyst 6. As the exhaust gas expands in the firstexpansion chamber 37, the back pressure and the exhaust noises arereduced. Note that, since the heat insulation chamber 39 is provided viathe downstream side separator 36, the exhaust gas having passed throughthe catalyst 6 and achieving high temperatures is blocked by the heatinsulation chamber 39, and therefore will not blow in the downstreamside cover 34. Thus, the downstream side cover 34 is prevented fromachieving high temperatures, and durability of the downstream side cover34 is enhanced.

Further, around the first expansion chamber 37, the sound absorptionchamber 42 where the sound absorbing material 43 is arranged is providedvia the inner sleeve 32. Therefore, the exhaust noises emitted from thefirst expansion chamber 37 are prevented from passing through the sleeveportion 30 and emitted to the outside of the exhaust muffler 2.

Next, as indicated by arrow E in FIG. 5, the exhaust gas passes througha pair of communication holes 351 c (see FIG. 4) provided at theupstream side separator 35, and arrives at the second expansion chamber38. The exhaust gas has its flow regulated when it passes through thecommunication holes 351 c, whereby the back pressure and the exhaustnoises are further reduced. Then, the exhaust gas having passed throughthe communication holes 351 c is expanded in the second expansionchamber 38, and the back pressure and the exhaust noises are even morereduced. In addition, since the second expansion chamber 38communicates, through the pores 322, with the sound absorption chamber42 formed around the second expansion chamber 38, the exhaust noises inthe second expansion chamber 38 are absorbed by the sound absorbingmaterial 43 arranged in the sound absorption chamber 42. Thus, theexhaust noise is still even more reduced.

Next, as indicated by arrow F in FIG. 5, the exhaust gas passes throughthe opening 412 a of the lid member 412 and flows into the exitcommunication pipe 41. The opening 412 a is burring shaped, and issmaller than the passage diameter of the pipe member 411. Therefore,when the exhaust gas flows into the exit communication pipe 41 from thesecond expansion chamber 38, the exhaust flow path is sharply narrowedby the opening 412 a, whereby the back pressure and the exhaust noisesof the exhaust gas are effectively reduced.

Note that, since the opening area S1 (see FIG. 9) of the opening 412 ais formed to be substantially as great as the cross-sectional area S2(see FIG. 2) of the exhaust flow path in the upstream end portion of theexhaust pipe 7, the exhaust flow path is prevented from excessivelynarrowed by the opening 412 a, and the exhaust flow path of proper sizeis secured.

Next, as indicated by arrow G in FIG. 5, the exhaust gas flows into theinner circumferential side of the spark arrester body portion 51 fromthe outer circumferential portion of the spark arrester body portion 51.When the exhaust gas passes through the spark arrester body portion 51,soot, carbon and the like in the exhaust gas are captured by themesh-like member of the spark arrester body portion 51.

Since the spark arrester body portion 51 is arranged in the exitcommunication pipe 41 being separated from the first and secondexpansion chambers 37 and 38, the back pressure with an exhaust pulse inthe first and second expansion chambers 37 and 38 will not act on thespark arrester body portion 51. Further, since the back pressure iseffectively reduced by the opening 412 a of the lid member 412, the backpressure acting on the spark arrester body portion 51 is sufficientlyreduced.

Note that, in the exit communication pipe 41, the passage area of theexhaust flow path formed around the spark arrester body portion 51, thatis, the difference between the cross-sectional area S3 (see FIG. 10) ofthe pipe member 411 and the cross-sectional area S4 (see FIG. 10) of thespark arrester body portion 51, is set to be substantially identical tothe opening area S1 (see FIG. 9) of the opening 412 a of the lid member412. Thus, while securing the passage area of the exhaust flow path inthe exit communication pipe 41, an excessive increase in the diameter ofthe pipe member 411 is avoided.

Finally, as indicated by arrow H in FIG. 5, the exhaust gas flows intothe tailpipe 52, and is discharged from the rear end portion of thetailpipe 52 into the air. In this manner, the exhaust gas dischargedfrom the exhaust portion 21 (see FIG. 2) of the engine 20 arrives at theexhaust muffler 2. Then, the exhaust gas is purified in the exhaustmuffler 2, and discharged from the tailpipe 52 into the air with fullysuppressed exhaust noises.

[Effects of Embodiment]

(1) The spark arrester body portion 51 is arranged in the exitcommunication pipe 41 separated from the first and second expansionchambers 37 and 38, and the lid member 412 having the opening 412 a asthe exhaust flow path narrowing portion is provided at the upstream endportion of the exit communication pipe 41. Accordingly, the backpressure and the exhaust pulse acting on the spark arrester body portion51 can be reduced. This can suppress deformation of the spark arresterbody portion 51. As a result, a reinforce member for reinforcing thespark arrester body portion 51 made of a mesh-like member can bedispensed with, and designing of the spark arrester can be streamlined.

(2) The spark arrester body portion 51 is structured solely by themesh-like member without any reinforce member and, therefore,productivity of the spark arrester body portion 51 can be improved and areduction in costs can be achieved.

(3) The spark arrester body portion 51 is structured without anyreinforce member. Thus, since the surface of the spark arrester bodyportion 51 is not shielded by the reinforce member, the filter portionof the spark arrester body portion 51 can be secured for the entiresurface. As a result, an increase in size of the spark arrester bodyportion 51 can be avoided, and the spark arrester body portion 51 can bestructured in a compact manner.

(4) The exhaust flow path narrowing portion can be easily formed by theburring-like opening 412 a provided at the lid member 412. Inparticular, as compared with the case where the tapered narrowingportion is formed as the exhaust flow path narrowing portion, theexhaust flow path can be sharply narrowed, whereby the back pressure andthe exhaust pulse in the exit communication pipe 41 can be moreeffectively reduced. Thus, deformation of the spark arrester bodyportion 51 can further be suppressed.

(5) The opening area S1 of the opening 412 a as the exhaust flow pathnarrowing portion is substantially identical to the cross-sectional areaS2 of the exhaust flow path at the upstream side end portion in theexhaust pipe 7. Thus, while realizing a reduction in the back pressureat the upstream side end portion of the exit communication pipe 41, itbecomes possible to secure the exhaust flow path of proper size and toavoid a reduction in engine performance caused by an excessive increasein the back pressure.

(6) The inner diameter of the pipe member 411 is set such that thedifference between the cross-sectional area S3 being perpendicular tothe exhaust flow path of the pipe member 411 and the cross-sectionalarea S4 being perpendicular to the exhaust flow path of the sparkarrester body portion 51 becomes substantially identical to the openingarea S1 of the opening 412 a. Thus, an excessive increase in the size ofthe pipe member 411 can be avoided, whereby the muffler body 3 can bestructured in a compact manner.

The present invention is not limited to the embodiment described above,and various modifications can be employed in the range not departingfrom the claims.

1. An exhaust muffler for a vehicle comprising: a muffler body coupled to an exhaust pipe; and a tailpipe coupled to the muffler body; wherein the muffler body includes: a plurality of expansion chambers; an exit communication pipe that discharges exhaust to the tailpipe from one of the plurality of expansion chambers positioned in a most downstream part of an exhaust flow path; an exhaust flow path narrowing portion at an upstream end of the exit communication pipe; and a spark arrester body arranged at a downstream side of the exhaust flow path narrowing portion in the exit communication pipe.
 2. The exhaust muffler for a vehicle according to claim 1, wherein the spark arrester body comprises a mesh-like member.
 3. The exhaust muffler for a vehicle according to claim 1, wherein the exhaust flow path narrowing portion is comprises a lid member having a through hole, the lid member being provided at an upstream portion of the exit communication pipe.
 4. The exhaust muffler for a vehicle according to claim 3, wherein an opening area of the through hole is substantially equal to a cross-sectional area of an exhaust flow path at an upstream end of the exhaust pipe.
 5. The exhaust muffler for a vehicle according to claim 3, wherein a difference between a cross-sectional area perpendicular to an exhaust flow path of the exit communication pipe and a cross-sectional area perpendicular to an exhaust flow path of the spark arrester is substantially equal to an opening area of the through hole.
 6. The exhaust muffler for a vehicle according to claim 1, wherein an upstream end of the spark arrester body is spaced apart from the exhaust flow path narrowing portion. 